"I was working on Chris’s album and I just came by to make sure everything was done properly," Banner tells Rolling Stone. "As soon as I walked in the studio, Justin and Chris were sitting there and said, ‘Hey, David Banner can do the beat!’"

Banner – producer behind tracks like Lil Wayne’s "La La" and T.I.’s "Rubberband Man" – crafted the song "Ladies Love Me" (listen below) for Brown’s new DJ Drama-assisted mixtape Boy In Detention, which hit the web on August 5th. As the trio recorded the track in a Los Angeles studio, Banner admits that Bieber’s prowess on the microphone really impressed him.

"Justin got in front of the mic and smashed," Banner says. "There were a couple mistakes but he went through the flow on the initial recording, the fast-rapping, in one take. Everybody in the studio was standing there with their mouths open."

Bieber revealed his lyrical skills late last year when a clip of the young pop star rapping under the moniker Shawty Mane appeared in a YouTube clip. Though fans later learned that Bieber’s lyrics were quite similar to another Canadian artist, Torey Lanez, Bieber's energy and delivery on the microphone was surprisingly on point.

"People try to take credit from him, but it was all him. Those boys work 10 times as hard as people give them credit for," Banner says.

Another surprise from the recording session: the genuine connection between Bieber and Brown. "I hope that people can feel the friendship that Justin and Chris have on the track," Banner says. "You can tell them really look out for each other."

In addition to "Ladies Love Me" and submitting tracks for Bieber’s next album, Banner also crafted "Crazy" on "Boy In Detention," and boasts of a new track he and Chris created for the "She Ain’t You" singer’s upcoming album: "Chris is moving to another level. You barely hear strong R&B records in the club anymore, unless they sound like rap records. Chris is definitely going to bring singing back to the club."